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Full text of "Text Book Of Mechanical Engineering"

744

Hydraulic Pressure Engine:

is then reversed. The principal feature in this engine is the
.crank pin B, which is not fixed, but capable of sliding to a limited
.amount, within a diametral groove in the crank plate c, being for
this purpose screwed into a shoe plate M. The power given to c
is transmitted by a hollow shaft Q, through the strong volute
spring H, to the driving pulley u. Now u is keyed to the inner
•shaft K, and when the load conies on the pulley there is a further
•coiling of spring H, which causes shaft K to turn relatively to G,

through an angle depending on the turning moment. The result
•of K'S turn is to rotate a cam F in such a way as to move the
•crank pin further from the shaft centre, and thus increase the
throw; while on the other hand a decrease in load reverses the
cam movement and enables the piston pressure to shorten the
crank centres. Now there are two ways of accommodating fluid
pressure to work required : alteration of stroke or of pressure. In
the steam engine reduced work is met by reduced pressure; but
•water, being inexpansible, can only be adjusted in supply by a

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